1. Field of the Invention
The present invention relates to an optical head apparatus used for an information reproducing apparatus to reproduce the information from the information recording medium by using a laser light or an information recording apparatus to record the information in the information recording medium.
2. Related Art
An optical head of the information reproducing apparatus to reproduce the recorded information through pits from an optical disk in which the pits to carry the information are formed in the high density, introduces the laser light emitted from a semiconductor laser element as a light source provided in the main body to an objective lens along a predetermined optical path, and a light beam condensed by the objective lens is irradiated onto the information recording surface of the optical disk, and a reflected light which is light modulated by the pit formed on the information recording surface, is introduced to a light receiving element by a predetermined optical path though the objective lens again, and in the light receiving element, by being converted into an electric signal corresponding to a received light amount, the recording information can be read.
In this connection, recently, a consideration of the optical disk in which the information can be recorded in the higher density as compared to the DVD, is conducted. In such the optical disk, because the pit on the information surface is formed smaller than the pit of the DVD, it is necessary that the light beam to read this is also formed to be a smaller spot.
When the numerical aperture of the objective lens is NA, and the wavelength of the light beam is λ, it is well known that the dimension (diameter) of the light spot is proportional to λ/NA. Accordingly, the shorter the wavelength of the light beam is, and the larger the numerical aperture NA of the objective lens is, the light spot can be made smaller.
However, from the relationship of thickness of the information recording medium, tilt (inclination) at the time of recording and reproducing or the tolerance value of the depth of focus of the light beam, when the numerical aperture is made so large, because the tolerance width of them becomes narrow, and exceeds the ability of the servo control, as the practical numerical aperture in the present situation, the NA is set to a value of about 0.6.
Accordingly, as a technology to increase the numerical aperture while maintaining the tolerance width, an optical head apparatus using a solid immersion lens (hereinafter, called SIL)is considered.
This is a technology in which the SIL is arranged between an objective lens and an optical disk, and a laser light condensed by the objective lens is irradiated onto the SIL, and after the laser light is further converged by the SIL and focused, it is irradiated onto the information recording surface of the optical lens. That is, the refraction by the SIL is used, and the apparent NA is increased, and a microscopic light spot is formed on the information recording surface of the optical disk.
FIG. 5 is a view showing an example of an optical head apparatus using the SIL. In FIG. 5, in a casing 100 of a pick-up P1, a magnet 101 for the focus control is provided, and a focus coil 102 is provided in the magnetic field generated by the magnet. The focus coil 102 is integrally fixed with a lens holder 104 to hold an objective lens 103.
The lens holder 104 is connected to the casing 100 through a support member 105 having the elasticity in the optical axis direction of the objective lens 103, and supported movably in the optical axis direction of the objective lens 103 by the casing 100.
A SIL 106 is a semi-spherical minute lens arranged in such a manner that a flat surface portion is opposed to the information recording surface of the optical disk, and on a slider 107, is fixedly supported so as to be coaxial to the objective lens 103. The slider 107 is elastically supported movably in the optical axis direction of the objective lens by being connected to the lens holder 104 through a support member 108 having the elasticity in the optical axis direction of the objective lens 103.
Further, the pick-up P1 is connected to a carriage 110 of the optical had apparatus through an arm 109. The carriage 110 is a movement mechanism to move the pick-up P1 supported by the arm 109 in the radial direction of the optical disk, and appropriately moves the pick-up P1 in the radial direction of the optical disk through the arm 109.
Further, when the optical disk is under the rotational condition, a thin layer of the air is formed between the disk surface and the SIL 106, and the SIL 106 is floated up with a predetermined distance h of about 100 nm.
FIG. 5 shows the optical head apparatus under the condition that the optical disk is rotated. The optical head apparatus adjusts the position of the objective lens 103 so that the distance in the optical axis direction between the SIL 106 which is currently floating, and the objective lens 103, becomes a predetermined distance by controlling the focus coil 102 by a control section, not shown. Thereby, the SIL 106 and the objective 107 are respectively arranged at appropriate optical positions in the focus direction from the information recording surface, and the laser light can be condensed onto the information recording surface of the optical disk as a minute optical spot.
(Problem that the Invention is to Solve)
As described above, in the optical head apparatus using the SIL 106, when the pick-up P1 reads the recording information from the rotating optical disk, because the distance between the bottom surface portion of the floating SIL 106 and the optical disk surface is kept to a very narrow distance h, for example, when, as shown in FIG. 5, there is a foreign material such as a dust which has the height H larger than this distance h on the disk surface or a protrusion due to the molding failure of the disk surface, the SIL 106 clashes against the foreign material, and in the worst case, there is a possibility that the SIL is damaged.